Piezoelectric device for ultrasonic sensor

ABSTRACT

A piezoelectric device includes a substrate with a cavity, a vibrating plate which is provided on the substrate so as to block an opening surface of the cavity, and a piezoelectric element which is provided on a surface of the vibrating plate opposite to the cavity, including a first electrode, a piezoelectric layer, and a second electrode, in which the second electrode has a laminated structure including a Pt layer (lower layer side electrode) and an Ir layer (upper layer side electrode), in which the Pt layer is in contact with the piezoelectric layer, and in which, if it is assumed that two directions which are parallel to a surface of the substrate and mutually perpendicular are defined as an X direction and a Y direction, the Ir layer is extended to an outside of the cavity at least in the X direction on an X-Y plane view.

BACKGROUND

1. Technical Field

The present invention relates to a piezoelectric device for anultrasonic sensor.

2. Related Art

In the related art, an ultrasonic sensor using electromechanicaltransformation characteristics of a piezoelectric element is provided.In the ultrasonic sensor, an ultrasonic wave (transmitting ultrasonicwave) is transmitted by driving the piezoelectric element by supplyingelectric signals to the piezoelectric element. In addition, thepiezoelectric element receives the ultrasonic wave (reflected ultrasonicwave) which is reflected from a measurement object, thereby driving thepiezoelectric element and obtaining the electric signals. In theultrasonic device equipped with the ultrasonic sensor, information(positions, shapes, or the like) relating to the measuring object isdetected based on these electric signals, that is, waveform signals ofthe transmitting ultrasonic wave or the reflected ultrasonic wave.

This type of the ultrasonic sensor is classified into a transmit-onlytype ultrasonic sensor optimized for transmitting the ultrasonic wave, areceive-only type ultrasonic sensor optimized for receiving theultrasonic wave, and a transmission-reception integral-type ultrasonicsensor optimized for both transmitting and receiving the ultrasonicwave. In addition, the ultrasonic sensor is also classified into a typeof the ultrasonic sensor in which the piezoelectric element side of avibrating plate is set to a passing area of the ultrasonic wave(so-called ACT surface type), a type of the ultrasonic sensor in which aside opposite to the piezoelectric element of the vibrating plate is setto the passing area of the ultrasonic wave (so-called CAV surface type),or the like.

Here, in a case where improvement in the receiving properties of theultrasonic sensor is obtained, from the viewpoint of obtaining highdeformation efficiency and excellent ferroelectricity, an increase inthe residual amount of polarization can be obtained by suppressing aninitial deflection to the CAV surface side of the vibrating plate. Thatis, it is preferable that the initial deflection of the vibrating plateis set to the ACT surface side instead of the CAV surface side bytensile stress. For example, in JP-A-2013-175879, a CAV surface typeultrasonic sensor in which iridium (Ir) is used for an upper electrodeis disclosed. The Ir has characteristics of great tensile stress. Byusing the characteristics, the initial deflection of the vibrating platecan be set to the ACT surface side instead of the CAV surface side bythe tensile stress. However, if the Ir is used as an electrode material,there is a possibility that the residual amount of polarization of thepiezoelectric element is reduced, and the receiving properties of theultrasonic sensor are deteriorated.

It can be also considered that platinum (Pt) which is used as theelectrode material in common with the Ir and which can greatly maintainthe residual amount of polarization of the piezoelectric element isapplied. However, the tensile stress of the Pt is lower than that of theIr, and the initial deflection to the CAV surface side of the vibratingplate becomes greater. Specifically, the piezoelectric element includinga piezoelectric layer which is formed by a chemical solution deposition(CSD) method especially has such tendency.

Accordingly, in a case where the Ir is applied as the electrode materialof the ultrasonic sensor, it can be expected that the deformationefficiency is improved by the tensile stress of the Ir. However, sincethe residual amount of polarization is reduced than a case where the Ptis applied as the electrode material of the ultrasonic sensor, there isa possibility that the receiving properties are deteriorated as aresult. On the other hand, in a case where the Pt is applied as theelectrode material, since the tensile stress of the Pt is smaller thanthat of the Ir, it is difficult to obtain high receiving properties.

SUMMARY

An advantage of some aspects of the invention is to provide apiezoelectric device for an ultrasonic sensor which is capable ofobtaining improvement in receiving properties.

An aspect of the invention is directed to a piezoelectric device for anultrasonic sensor including: a substrate with a cavity; a vibratingplate which is provided on the substrate so as to block an openingsurface of the cavity; and a piezoelectric element which is provided ona surface of the vibrating plate opposite to the cavity, including afirst electrode, a piezoelectric layer which is provided on the firstelectrode, and a second electrode which is provided on the piezoelectriclayer, and in which the second electrode has a laminated structureincluding a platinum layer and an iridium layer, in which the platinumlayer is in contact with the piezoelectric layer, and in which, if it isassumed that two directions which are parallel to a surface of thesubstrate and mutually perpendicular are defined as an X direction and aY direction, the iridium layer is extended to an outside of thepiezoelectric element and the cavity at least in the X direction on anX-Y plane view.

According to the aspect, it is expected that the residual amount ofpolarization is increased by contacting the platinum layer to thepiezoelectric layer, thereby improving ferroelectricity. In addition, itis possible to improve deformation efficiency by suppressing an initialdeflection to the CAV surface side of the vibrating plate by a tensilestress of the iridium layer. Accordingly, it is possible to improvereceiving properties of the piezoelectric device for an ultrasonicsensor.

In the piezoelectric device for an ultrasonic sensor, the piezoelectriclayer may be present in the cavity, and the platinum layer may bepresent only on the piezoelectric layer in the X direction.

According to this configuration, when a thermal treatment is performedfor forming a good interface in the piezoelectric element, it ispossible to prevent the iridium layer at least on a platinum electrodefrom being separated.

Here, in the piezoelectric device for an ultrasonic sensor, it ispreferable that a second iridium layer is extended to the outside of thepiezoelectric element and the cavity in a Y direction on the X-Y planeview, and the second iridium layer is separated from the iridium layer,on the piezoelectric layer.

According to this configuration, since the tensile stress of the iridiumlayer is acted in not only the X direction but also the Y direction, itis possible to more suppress the initial deflection to the CAV surfaceside of the vibrating plate. Accordingly, the receiving properties ofthe piezoelectric device for an ultrasonic sensor can be improved.

In the piezoelectric device for an ultrasonic sensor, the piezoelectriclayer may be present in the cavity, and the second iridium layer may beextended from a both end portions on the piezoelectric layer to theoutside of the cavity in the Y direction, and a second platinum layerwhich is separated from the platinum layer may be present between theboth end portions of the piezoelectric layer and the second iridiumlayer.

According to this configuration, it is possible to prevent thedisconnection between the electrodes by preventing the separation of thesecond iridium layer after being subjected a thermal treatment (recoveryanneal (RA) treatment) of the piezoelectric element.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a cross-sectional view illustrating a configuration example ofan ultrasonic device.

FIG. 2 is an exploded perspective view illustrating a configurationexample of an ultrasonic sensor.

FIG. 3 is a plane view illustrating the configuration example of theultrasonic sensor.

FIG. 4 is a cross-sectional view illustrating the configuration exampleof the ultrasonic sensor.

FIG. 5 is a cross-sectional view illustrating the configuration exampleof the ultrasonic sensor.

FIG. 6 is a plane view illustrating the manufacturing example of theultrasonic sensor.

FIG. 7 is a cross-sectional view illustrating the manufacturing exampleof the ultrasonic sensor.

FIG. 8 is a cross-sectional view illustrating the manufacturing exampleof the ultrasonic sensor.

FIG. 9 is a plane view illustrating the manufacturing example of theultrasonic sensor.

FIG. 10 is a cross-sectional view illustrating the manufacturing exampleof the ultrasonic sensor.

FIG. 11 is a cross-sectional view illustrating the manufacturing exampleof the ultrasonic sensor.

FIG. 12 is a plane view illustrating the manufacturing example of theultrasonic sensor.

FIG. 13 is a cross-sectional view illustrating the manufacturing exampleof the ultrasonic sensor.

FIG. 14 is a cross-sectional view illustrating the manufacturing exampleof the ultrasonic sensor.

FIG. 15 illustrates a measurement result of a P-E loop of Example 1.

FIG. 16 illustrates a measurement result of a P-E loop of Example 3.

FIG. 17 illustrates a measurement result of a P-E loop of ComparativeExample 2.

FIG. 18 illustrates a measurement result of a P-E loop of ComparativeExample 6.

FIG. 19 is a schematic diagram illustrating a convex deflection of adevice element.

FIG. 20 is a schematic diagram illustrating a concave deflection of adevice element.

FIG. 21 is an explanatory diagram of an evaluation method oftransmitting and receiving properties.

FIG. 22 illustrates a measurement result of transmitting and receivingproperties of Example 2 and Comparative Example 3.

FIG. 23 illustrates a measurement result of transmitting and receivingproperties of Example 4 and Comparative Example 7.

FIG. 24 illustrates a simulation result of a relationship between adeflection shape and the transmitting and receiving properties.

FIG. 25 is a perspective view illustrating an example of an ultrasonicdiagnosis device.

FIG. 26 is a front view illustrating an example of an ultrasonic probe.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described withreference to drawings. The following descriptions are intended to showan aspect of the invention, and can be arbitrarily changed within arange not departing from the gist of the invention. Note that, the samemembers or parts are denoted by the same numerals in the drawings, andthe description thereof will not be repeated appropriately. In addition,in FIGS. 2 to 14, X, Y, and Z indicate three mutually perpendicularspatial axes. In the present specification, each of directions along theaxes will be described as a first direction X (X direction), a seconddirection Y (Y direction), and a third direction Z (Z direction). The Xdirection and the Y direction indicate in-plane directions of a plate, alayer, and a film, and the Z direction indicates a thickness directionor a lamination direction of the plate, the layer, and the film.

Embodiment 1 Ultrasonic Device

FIG. 1 is a cross-sectional view illustrating a configuration example ofan ultrasonic device equipped with an ultrasonic sensor. As illustratedin the drawings, an ultrasonic probe I is configured by equipped with aCAV surface type ultrasonic sensor 1, a flexible printed circuit board(FPC board 2) which is connected to the ultrasonic sensor 1, a cable 3extracted from a device terminal (not illustrated), a relay substrate 4for connecting between the FPC board 2 and the cable 3, a housing 5 forcovering the ultrasonic sensor 1, the FPC board 2, and the relaysubstrate 4, a water-resistant resin 6 for filling between the hosing 5and the ultrasonic sensor 1, or the like.

The ultrasonic waves are transmitted from the ultrasonic sensor 1. Inaddition, the ultrasonic waves which are reflected from the measurementobject are received by the ultrasonic sensor 1. In the device terminalof the ultrasonic probe I, information (position, shape, or the like)relating to the measurement object is detected based on waveform signalsof these ultrasonic waves.

According to the ultrasonic sensor 1, the occurrence of distortion inthe structure can be suppressed and high reliability can be maintainedas described below. Accordingly, by equipping the ultrasonic sensor 1,the ultrasonic device with excellent various characteristics can beobtained. The invention can also be applied to any of the ultrasonicsensor of a transmit-only type ultrasonic sensor optimized fortransmitting the ultrasonic wave, a receive-only type ultrasonic sensoroptimized for receiving the ultrasonic wave, and atransmission-reception integral-type ultrasonic wave optimized for bothtransmitting and receiving the ultrasonic wave. The ultrasonic devicewhich can equip the ultrasonic sensor 1 is not limited to the ultrasonicprobe I.

Ultrasonic Sensor

Next, a configuration example of the ultrasonic sensor 1 will bedescribed. FIG. 2 is an exploded perspective view illustrating theultrasonic sensor. FIG. 3 is a plane view illustrating a substrate ofthe ultrasonic sensor. FIG. 4 is a cross-sectional view taken along theline A-A′ in FIG. 3. FIG. 5 is a cross-sectional view taken along theline B-B′ in FIG. 3.

As illustrated in FIGS. 1 and 2, the ultrasonic sensor 1 is configuredby including an ultrasonic sensor element 310, a sound adjustment layer13, a lens member 20, and a surrounding plate 40. The ultrasonic sensorelement 310 is configured by including a substrate 10, a vibrating plate50, and a piezoelectric element 300. In the ultrasonic sensor element310, in addition to the surrounding plate 40, the sound adjustment layer13 and the lens member 20 are provided, thereby providing the ultrasonicsensor 1. In FIG. 2, the surrounding plate 40 and a supporting member 41are separately illustrated. However, the both are integrally configuredin practice.

A plurality of partitions 11 are formed on the substrate 10. A pluralityof spaces 12 are partitioned by the plurality of partitions 11. In thesubstrate 10, a Si monocrystalline substrate can be used. In thesubstrate 10, it is not limited to the above-described example, a SOIsubstrate, a glass substrate, or the like may be used.

The space 12 is formed so as to passing the substrate 10 in the Zdirection. A plurality of spaces 12 are formed two dimensionally, thatis, are formed in the X direction and are formed in the Y direction.When the X direction is set as a scan direction and the Y direction isset as a slice direction, the ultrasonic sensor 1 transmits and receivesthe ultrasonic waves for each row extending to the slice direction whilescanning in the scan direction. Accordingly, sensing information in theslice direction can be continuously obtained in the scan direction. Thespace 12 has a square shape when viewed from the Z direction (a lengthratio of the X direction to the Y direction is 1:1).

An arrangement or a shape of the space 12 can be variously changed. Forexample, the plurality of spaces 12 may be formed on dimensionally, thatis, may be formed in any one direction of the X direction and the Ydirection. In addition, the space 12 may have a rectangular shape whenviewed from the Z direction (other than 1:1 of a length ratio of the Xdirection to the Y direction).

The vibrating plate 50 is provided on the substrate 10 so as to blockthe space 12. Hereinafter, a surface of the substrate 10 side of thevibrating plate 50 referred to as a first surface 50 a and a surfacefacing the first surface 50 a is referred to as a second surface 50 b.The vibrating plate 50 is configured of an elastic film 51 formed on thesubstrate 10 and an insulation layer 52 which is formed on the elasticfilm 51. In this case, the first surface 50 a is configured by theelastic film 51 and the second surface 50 b is configured by theinsulation layer 52.

The elastic film 51 is formed of silicon dioxide (SiO₂) or the like andthe insulation layer 52 is formed of zirconium oxide (ZrO₂) or the like.The elastic film 51 may not be the different member from the substrate10. For example, a part of the substrate 10 is processed thin and theresultant may be used as the elastic film 51. A total thickness of thevibrating plate 50 and the substrate 10 is about 50 μm. However, thevalue is not limited thereto. The total thickness of the vibrating plate50 and the substrate 10 can be appropriately selected by consideringflexibility, a strength or the like.

The piezoelectric element 300 for transmitting and/or receiving theultrasonic waves is provided on a portion corresponding to the space 12on the second surface 50 b side of the vibrating plate 50. Here, aportion corresponding to the space 12 on the second surface 50 b side ofthe vibrating plate 50 is referred to as a movable portion. The moveableportion is a portion in which vibrating occurs by the deformation of thepiezoelectric element 300. The ultrasonic waves are transmitted and/orreceived from the ultrasonic sensor 1 in accordance with the vibrationsoccurred in the moveable portion.

The sound adjustment layer 13 is provided in the space 12. By providingthe sound adjustment layer 13, it is possible to prevent acousticimpedance from being rapidly changed between the piezoelectric element300 and the measurement object. As a result, it is possible to preventpropagation efficiency of the ultrasonic wave from being deteriorated.The sound adjustment layer 13 can be configured from a silicone resin,for example. However, it is not limited to the example, and the materialin accordance with the purpose of the ultrasonic sensor can beappropriately selected and can be used.

The lens member 20 is provided on the side opposite to the vibratingplate 50 of the substrate 10. The lens member 20 has a function forconverging the ultrasonic waves. In a case where the ultrasonic wavesare converged by an electronic focusing method, or the like, the lensmember 20 can be omitted. Here, the sound adjustment layer 13 has anadhesion function between the lens member 20 and the substrate 10. Theultrasonic sensor 1 is configured by intervening the sound adjustmentlayer 13 between the lens member 20 and the substrate 10 (partitions11).

When the lens member 20 is mounted on the ultrasonic sensor element 310or when adhesiveness of the lens member 20 is maintained after mountingthe lens member 20, the lens member 20 is pressed to the soundadjustment layer 13 side, in some cases. Even in a case where the lensmember 20 is not equipped or a case where the other member is providedinstead of the lens member, in order to maintain the adhesiveness ofeach portion, the pressing force is applied to the vibrating plate 50from the sound adjustment layer 13 side in some cases. Since theultrasonic sensor 1 is configured by providing with the supportingmember 41, as described above, it is possible to suppress the structuraldistortion even when the a predetermined external force is applied tothe vibrating plate 50, and thus high reliability can be maintained.

In the CAV type ultrasonic device 1 is configured in which the sideopposite to the piezoelectric element 300 of the vibrating plate 50becomes the passing area of the ultrasonic waves. According to this,since a configuration in which the moisture from the outside isextremely difficult to reach the piezoelectric element 300 can beobtained, the ultrasonic sensor 1 with excellent electrical safety inuse is provided. In addition, in a case where the piezoelectric element300 and the vibrating plate 50 are a thin film, an edge portion 40 a ofthe surrounding plate 40 having a sufficient thickness than thevibrating plate 50 and the supporting member 41 are bonded or adhered tothe vibrating plate 50 so as to surround the piezoelectric element 300.Therefore, handling properties during manufacturing can be improved,thereby facilitating the handling of the ultrasonic sensor 1.

As illustrated in FIGS. 3 to 5, the piezoelectric element 300 isconfigured by including a first electrode layer 60, a piezoelectriclayer 70, and a second electrode layer 80. The thickness of each layeris not particularly limited and can be appropriately selected accordingto the ultrasonic sensor 1 to be applied.

The first electrode layer 60 is extended in the Y direction and thesecond electrode layer 80 is extended in the X direction over theplurality of piezoelectric elements 300. Accordingly, the piezoelectricelement 300 can be selected for each row of the first electrode layer 60or for each row of the second electrode layer 80 and transmitting andthe receiving of the ultrasonic waves are performed for each rowextending to the slice direction (Y direction) while scanning in theabove-described scan direction (X direction). Here, in the piezoelectricelement 300, a portion where the first electrode layer 60 and the secondelectrode layer 80 are overlapped in the Z direction is referred to as afunctional portion. The functional portion is a region to be driven byapplying the voltage by the selected first electrode layer 60 and secondelectrode layer 80, and present within the above-described movableportion.

In addition, in the present embodiment, at least the vibrating plate 50and the first electrode layer 60 are displaced by the displacing thepiezoelectric layer 70. That is, in the present embodiment, at least thevibrating plate 50 and the first electrode layer 60 have a function as avibrating plate, substantially. However, any one or the both of elasticfilm 51 and the insulation layer 52 are not provided, and only the firstelectrode layer 60 may function as the vibrating plate. In a case wherethe first electrode layer 60 is directly provided on the substrate 10,the first electrode layer 60 is protected by an insulating protectionfilm is preferable.

The piezoelectric layer 70 configuring the piezoelectric element 300 isin the region inner side of the space 12, when viewed from the Zdirection. That is, any of the X direction and the Y direction of thepiezoelectric layer 70 is shorter than that of the space 12. However, acase where the X direction of the piezoelectric layer 70 is longer thanthat of the space 12, or a case where the Y direction of thepiezoelectric layer 70 is longer than that of the space 12 is includedin the invention. The space 12 in which the X direction and the Ydirection are appropriately changed based on the X direction and the Ydirection of the piezoelectric layer 70 also permitted.

As illustrated in FIGS. 2 to 5, the surrounding plate 40 is provided onthe second surface 50 b side of the vibrating plate 50. A concaveportion (piezoelectric element holding portion 32) is formed at thecenter of the surrounding plate 40, and around the piezoelectric elementholding portion 32 is surrounded by the edge portion 40 a and a surface40 b of the surrounding plate 40. A region around the piezoelectricelement 300 (region including the top surface and the side surface ofthe piezoelectric element 300) is covered with the piezoelectric elementholding portion 32. Accordingly, the top surface of the piezoelectricelement 300 is covered with the surface 40 b of the surrounding plate40, and the side surface is covered with the edge portion 40 a.

The surrounding plate 40 is bonded to the ultrasonic sensor element 310side in the edge portion 40 a. For bonding of the surrounding plate 40,an adhesive (not illustrated) can be used. However, it is not limited tothe example. The length of the piezoelectric element holding portion 32in the Z direction is about 80 μm. However, it is not limited to thevalue. The length of the piezoelectric element holding portion 32 may bea value by which a space which does not inhibit the driving thepiezoelectric element 300 is maintained. In addition, the piezoelectricelement holding portion 32 may be filled with air and may be filled witha resin. The thickness of the surrounding plate 40 is about 400 μm.However, it is not limited to the value.

In the ultrasonic sensor 1, the supporting member 41 is provided betweenthe surface 40 b on the piezoelectric element 300 side of thesurrounding plate 40 and the second surface 50 b of the vibrating plate50, and the vibrating plate 50 is supported by the supporting member 41.Accordingly, for example, when the lens member 20 is mounted to thesubstrate 10 or when adhesiveness of the substrate 10 and the lensmember 20 is maintained, the vibrating plate 50 is prevented from beinggreatly deflected in the piezoelectric element holding portion 32, evenwhen a predetermined pressure is added from the sound adjustment layer13 side to the vibrating plate 50. Accordingly, the structure distortioncan be suppressed, and the high reliability can be maintained.

Furthermore, the supporting member 41 is provided on a position notoverlapping the piezoelectric element 300. Therefore, the piezoelectricelement 300 is avoided from being excessively restrained by thesupporting member 41. Accordingly, as compared to a case where thesupporting member 41 is not provided, the transmitting efficiency orreceiving efficiency of the ultrasonic waves is prevented from beingexcessively deteriorated.

A position not overlapping the piezoelectric element 300 is a positionnot overlapping the above-described functional portion (a portionsandwiched by the first electrode layer 60 and the second electrodelayer 80), when viewed from the Z direction. Specifically, in theultrasonic sensor 1, the supporting member 41 having a width narrowerthan the partitions 11 is provided between the spaces 12 adjacent in theY direction. That is, the supporting member 41 is not overlapped to eventhe above-described moveable member (a portion corresponding to thespace 12 on the second surface 50 b side of the vibrating plate 50),when viewed from the Z direction. Therefore, as compared to a case wherethe supporting member 41 is not provided, the transmitting efficiency orreceiving efficiency of the ultrasonic waves is reliably prevented frombeing deteriorated. The supporting member 41 is bonded to the ultrasonicsensor element 310 side by the adhesive (not illustrated). However, themethod of the bonding is not limited to the example.

The supporting member 41 has a beam shape extending along the Xdirection. Therefore, the vibrating plate 50 can be supported in a widerrange over the X direction. The beam shaped supporting member 41 may beextended along the Y direction instead of X direction. In the beamshaped supporting member 41, an end portion of extending one side may beseparated from the edge portion 40 a of the surrounding plate 40. If theend portion of at least one side in the extending direction is incontact with the edge portion 40 a of the surrounding plate 40, thisstructure is included in the beam shaped supporting member 41.

The beam shaped supporting member 41 is manufactured by wet etching thesurrounding plate 40. As described above, the supporting member 41 ismanufactured by taking advantage of the configuration material of thesurrounding plate 40 and has the same configuration as that of thesurrounding plate 40. In the wet etching, processing accuracy isdeteriorated as compared to a dray etching, but a lot of the region canbe eliminated at a short time, therefore the wet etching is anappropriate method for manufacturing the beam shaped supporting member41.

The center portion of the piezoelectric element holding portion 32 iscomparatively separated from the edge portion 40 a of the surroundingplate 40. Accordingly, in the vibrating plate 50, a center location Ccorresponding to the center portion of the piezoelectric element holdingportion 32, rigidity is easily lowered in a case where the supportingmember 41 is not provided. The supporting member 41 is provided at thecenter portion of the piezoelectric element holding portion 32 so as tosupport the center location C of the vibrating plate 50. Accordingly,higher reliability can be maintained.

In the invention, the number, the arrangement, the shape, or the like ofthe supporting members 41 can be variously selected. For example, thenumber of the supporting members 41 may be plural. In this case, it ispreferable that the supporting member 41 is provided at an equalinterval in the piezoelectric element holding portion 32. According tothis, the vibrating plate 50 can be uniformly supported. Accordingly, itis preferable that the number of the vibrating plates 50 is an oddnumber equal to or greater than three. The reason is that when thesupporting member 41 is provided at the equal interval in thepiezoelectric element holding port ion 32, the center supporting member41 is positioned adjacent to the center location C of the vibratingplate 50. For example, when the number of the supporting members 41 isabout 3, the balance is good.

The supporting member 41 may not have a beam shape. The supportingmember 41 may be provided only on a portion shifting from the centerlocation C of the vibrating plate 50. The supporting member 41 may notbe a linear shape in the extending direction. Depending on themanufacturing method of the supporting member 41, there is a case thecross-section area of the supporting member 41 in the X-Y plane isdifferent according to the Z direction.

The piezoelectric layer 70 is configured by patterning for each space12, and pinched by the first electrode layer 60 and the second electrodelayer 80. The piezoelectric layer 70 is configured by including acomplex oxide having an ABO₃ type perovskite structure, for example. AnA site having the ABO₃ type perovskite structure forms to have oxygen12-coordinated, and a B site having oxygen 6-coordinated and the sitesform an octahedron.

As the complex oxide configuring the piezoelectric layer 70, a PZT basedcomplex oxide in which the piezoelectric properties are comparativelyhigh, and lead (Pb), zirconium (Zr), and titanium (Ti) are included. Byusing the PZT based complex oxide, improvement in the displacement ofthe piezoelectric element 300 can be easily obtained. In addition, inaddition to this, a PMN-PT based complex oxide including lead, magnesium(Mg), niobium (Nb), and titanium can also be applied.

In addition, as the complex oxide configuring the piezoelectric layer70, a non-lead based material with reduced content of the lead can beused. As the non-lead based material, for example, a BFO complex oxideincluding bismuth (Bi) and iron (Fe), a BF-BT based complex oxideincluding bismuth, barium (Ba), iron, and titanium, a BFM-BT basedcomplex oxide including bismuth, iron, manganese (Mn), barium, andtitanium, a KNN based complex oxide including potassium (K), sodium(Na), and niobium, or the like is included. By using the non-lead basedmaterial, since the content of the lead of the piezoelectric layer 70can be suppressed, the ultrasonic sensor 1 by which the load to theenvironment is small can be configured.

In these complex oxides, the other elements may be included. As theother element, lithium (Li), bismuth, barium, calcium (Ca), strontium(Sr), samarium (Sm), Cerium (Ce), or the like to be substituted to apart of the A site of the piezoelectric layer 70, or manganese, zinc(Zn), zirconium, magnesium, copper (Cu), aluminum (Al), nickel (Ni),cobalt (Co), chromium (Cr), titanium, zirconium, or the like to besubstituted to a part of the B site of the piezoelectric layer 70 isincluded.

The complex oxide having the ABO₃ type perovskite structure includes acomplex oxide shifted from a stoicheiometric composition due to adeficiency or excess or a complex oxide in which a part of the elementis substituted to the other element. That is, as long as a complex oxidehas the perovskite structure, shifting of inevitable composition due tolattice mismatch, oxygen deficiency, or the like, and also a part of theelement substitution or the like are acceptable.

The piezoelectric layer 70 may have a laminate structure formed from theplurality of complex oxide or the other materials. For example, anadhesion layer such as a Ti layer is provided on an uppermost layer anda lowermost layer, and it may be used as the piezoelectric layer 70.Alternatively, each of an underlayer and a main layer which are formedof the complex oxide is provided, and for example, a control layer forimproving orientation of the crystal may be provided between theselayers. Such a control layer can be configured from a titan oxide(TiO_(x)) layer or the like, for example. Of course, each of adhesionlayers may be provided on the uppermost layer and the lowermost layer ofthe underlayer or the main layer.

The material of the first electrode layer 60 is not limited as long asit has the conductivity. As the material of the first electrode layer60, a metal material, a tin-based conductive material oxide, a zincoxide-based conductive material, an oxide conductive material, or thelike is included. As the metal material, platinum (Pt), iridium (Ir),gold (Au), aluminum (Al), copper (Cu), titanium (Ti), stainless steel,or the like is included. The tin-based conductive material oxide is anindium tin oxide (ITO), a fluorine-doped tin oxide (FTC), or the like.The oxide-based conductive material is a zinc oxide-based conductivematerial, a strontium ruthenium oxide (SrRuO₃), a nickel lanthanum(LaNiO₃), an element-doped strontium titanate, or the like. The materialof the first electrode layer 60 may be a conductive polymer. Inaddition, the first electrode layer 60 may have a laminate structureformed from a plurality of materials. For example, an adhesion layersuch as a Ti layer is provided to an uppermost layer and a lowermostlayer, and it may be used as the first electrode layer 60. In a casewhere the adhesion layer is provided to the lowermost layer which isprovided between the piezoelectric element 300 and the vibrating plate50, the material thereof is not limited thereto, a material such astitanium oxide (TiO_(x)) or silicon nitride (SiN) may be used.

In the invention, the second electrode layer 80 has a laminate structureincluding a lower layer side electrode 80 a formed of platinum (Pt) andan upper layer side electrode 80 b which is formed of iridium (Ir). Thatis, the lower layer side electrode 80 a formed of the Pt is in contactwith the piezoelectric layer 70. Accordingly, a residual amount ofpolarization of the piezoelectric layer 70 is increased, and it isexpected that the ferroelectricity is improved. As a result, theultrasonic sensor 1 in which the piezoelectric element 300 in which thelower layer side electrode 80 a formed of the Pt is in contact with thepiezoelectric layer 70 is applied can obtain the good receivingproperties.

Here, the lower layer side electrode 80 a is present on thepiezoelectric layer 70 (refer to FIG. 5), the upper layer sideelectrodes 80 b cover the side surface of the piezoelectric layer 70from the top of the lower layer side electrode 80 a, are continuouslyprovided on the insulation layer 52 configuring the vibrating plate 50between the piezoelectric layers 70, and are extended in the X direction(refer to FIG. 5). The lower layer side electrodes 80 a may becontinuously provided in the X direction.

In addition, as illustrated in FIG. 4, the lower layer side electrode 80a and the upper layer side electrode 80 b are provided only on thecenter portion of the piezoelectric layer 70 in the Y direction. Thatis, the upper layer side electrode 80 b on the piezoelectric layer 70 isformed through the lower layer side electrode 80 a.

Accordingly, although details will be described later, when a thermaltreatment for forming the good interface in the piezoelectric element300 is performed, it is possible to prevent the upper layer sideelectrode 80 b which is formed of the Ir on at least the lower layerside electrode 80 a which is formed of the Pt from being separated.

Furthermore, on the both end portions of each piezoelectric layer 70 inthe Y direction, a Pt layer 81 a and an Ir layer 81 b which areconfigured at the same layer as that of the lower layer side electrode80 a and the upper layer side electrode 80 b are provided, and only theIr layer 81 b is extended on the first electrode layer 60 between thepiezoelectric layers 70 by covering the side surface of thepiezoelectric layer 70, and extended to the end portion of the adjacentpiezoelectric layer 70.

Such the Pt layer 81 a and the Ir layer 81 b are formed at the same timeof the lower layer side electrode 80 a and the upper layer sideelectrode 80 b, and are separated by the patterning. That is, bypatterning, the Pt layer 81 a and the Ir layer 81 b are separated fromthe both side end portions of the lower layer side electrode 80 a andthe upper layer side electrode 80 b in the Y direction at a distance L.The distance L is about 5 μm. However, it is not limited thereto. The Irlayer 81 b may not always be provided.

That is, as illustrated in FIG. 3, in the second electrode layer 80, atleast the upper layer side electrode 80 b which is formed of the Ir isconfigured by patterning to a shape which is extended to the outside ofthe piezoelectric element 300 and the space 12 (cavity) at least in theX direction. According to the configuration, deformation efficiency canbe improved by suppressing the initial deflection to the CAV surfaceside of the vibrating plate 50 due to the tensile stress of the upperlayer side electrode 80 b formed of the Ir, and the ultrasonic sensor 1to which the piezoelectric element 300 is applied can obtain theexcellent receiving properties.

In addition, from the viewpoint of the further improvement in thedeformation efficiency, the Ir layer 81 b is extended to the outside ofthe piezoelectric element 300 and the space 12 in the Y direction, andon the piezoelectric layer 70, it is preferable that a part thereof isconfigured by patterning into a shape separated from the upper layerside electrode 80 b. That is, a tensile stress of the Ir layer 81 bwhich is extended to the outside of the piezoelectric element 300 andthe space 12 in the Y direction is added to the tensile stress of theupper layer side electrode 80 b which is extended to the outside of thepiezoelectric element 300 and the space 12 in the X direction. Accordingto the configuration, since the tensile stress of the Ir is also actedon not only the X direction, but also the Y direction with respect tothe piezoelectric element 300, the initial deflection to the CAV surfaceside of the vibrating plate 50 can further be suppressed.

As described above, the Pt layer 81 a which is separated from the lowerlayer side electrode 80 a is present between the both end portions ofthe piezoelectric layer 70 and the Ir layer 81 b. According to theconfiguration, it is possible to prevent the disconnection between theelectrodes by preventing the separation of the Ir layer 81 b after beingsubjected a thermal treatment (recovery anneal (RA) treatment) of thepiezoelectric element 300 to be described.

The other layer which is formed of the above-described materialincluding conductivity may be provided between the layers of the lowerlayer side electrode 80 a and the upper layer side electrode 80 b. In acase of forming the upper layer side electrode 80 b having the laminatestructure, in the same manner as that of the above-described firstelectrode layer 60, the adhesion layer such as a Ti layer is provided onan uppermost layer and a lowermost layer, and it may be used as theupper layer side electrode 80 b. The adhesion layer which is provided onthe uppermost layer of the upper layer side electrode 80 b is providedfor overlapping lead wirings by gold (Au), silver (Ag), copper (Cu),nickel (Ni), nickel-chromium (Ni—Cr), titanium-tungsten (Ti—W), or thelike. In addition, in a case where the wiring is formed by plating, aseed layer such as palladium (Pd) may be formed instead of the adhesionlayer. Alternatively, a protecting film such as an aluminum oxide(Al₂O₃), a tantalum oxide (Ta₂O₅), a silicon dioxide (SiO₂), or the likemay be provided.

In the present embodiment, from the viewpoint of a RA treatment to bedescribed, it is preferable that the other layer is not intervenedbetween the piezoelectric layer 70 and the second electrode layer 80.However, if it is the degree not affect to the RA treatment, it ispermitted that the other layer is partially intervened. As the otherlayer, a metal layer such as gold (Au), silver (Ag), titanium (Ti),copper (Cu), or nickel (Ni); an alloy layer such as nickel-chromium(Ni—Cr) or titanium-tungsten (Ti—W); and a conductive oxide layer suchas nickel lanthanum (LaNiO₃; LNO) or ruthenium acid strontium (SrRuO₃;SRO) are included.

Manufacturing Method

Next, an example of the manufacturing method of the ultrasonic sensor 1will be described. FIGS. 6 to 14 mainly illustrate a process of amanufacturing method of a side on the ultrasonic sensor element. FIGS.6, 9, and 12 are plane views of the ultrasonic sensor element whenviewed from the Z direction. FIG. 7 is a cross-sectional view takenalong the line C-C′ in FIG. 6, and FIG. 8 is a cross-section view takenalong the line D-D′ in FIG. 6. FIG. 10 is a cross-section view takenalong the line E-E′ in FIG. 9, and FIG. 11 is a cross-section view takenalong the line F-F′ in FIG. 9. FIG. 13 is a cross-section view takenalong the line G-G′ in FIG. 12, and FIG. 14 is a cross-section viewtaken along the line H-H′ in FIG. 12.

Firstly, as illustrated in FIGS. 6 to 8, the elastic film 51 which isformed of silicon dioxide (SiO₂) is formed on the surface of the siliconmade substrate 10 (hereinafter, referred to as a “wafer 110”) by thethermal oxidation or the like. Thereafter, a film of zirconium (Zr) isformed on the elastic film 51 by a sputtering method, the insulationlayer 52 which is formed of zirconium oxide (ZrO₂) is formed by thethermal oxidation, and the resultant is set as the vibrating plate 50.The first electrode layer 60 is formed on the insulation layer 52 by thesputtering method or an evaporation method. At this time, the firstelectrode layer 60 having a laminate structure formed from the same typeof the electrode layers or the different type of the electrode layersmay be formed.

Next, as illustrated in FIGS. 9 to 11, the piezoelectric layer 70 isformed on the first electrode layer 60 and the formed piezoelectriclayers 70 are subjected to the patterning into a predetermined shape.For example, the piezoelectric layer 70 is formed by using a chemicalsolution deposition (CSD) method in which a metallic complex is coatedwith a solution which is dissolved and dispersed to a solvent and isdried, and further burned at a high temperature to obtain apiezoelectrode material which is formed of a metal oxide. The method isnot limited to the CSD method, and a sol-gel method, a laser ablationmethod, a sputtering method, a pulse laser deposition method (PLDmethod), a CVD method, an aerosol deposition method, or the like may beused.

The detailed forming procedure example in a case where the piezoelectriclayer 70 is formed by the CSD method is as follows. That is, a precursorsolution which is formed of a metal-organic decomposition (MOD) solutionor sol including the metallic complex and is used for forming thepiezoelectric layer 70 is prepared. The precursor solution is appliedonto the first electrode layer 60 by using a spin coating method to forma precursor film (not illustrated) (coating process). The precursor filmis heated at a predetermined temperature and dried for the certain time(drying process), is further heated the dried precursor film at thepredetermined temperature, and is delipidated by maintaining for thecertain time (degreasing process). The precursor film is crystallized byheating and maintaining the precursor film and to form the piezoelectriclayer 70 (burning process). The piezoelectric layer 70 formed by the CSDmethod has a plurality of piezoelectric films which are formed by aseries of process from the coating process to the burning process. Thatis, the piezoelectric layer 70 is formed by repeating the series ofprocess from the coating process to the burning process in plural times.In the series of process from the coating process to the burningprocess, after repeating the processes from the coating process to thedegreasing process in plural times, the burning process may beperformed.

A layer or the film formed by the CSD method has an interface. In thelayer or the film formed by the CSD method, remains of the coating orthe burning are remained, and such the remains becomes a confirmable“interface” by observing the cross-section or analyzing theconcentration distribution of the element in the layer (or in the film).The “interface” strictly means a boundary between the layers or thefilms, and in here, means adjacent to the boundary between the layers orthe films. In a case of observing the cross-section of the layer or thefilm formed by a wet method, such an interface is confirmed as a portionhaving a dark color than the other portion, or a portion having a thincolor than the other portion in the vicinity of the boundary to anadjacent layer or film. In addition, in a case where the concentrationdistribution of the element is analyzed, the interface is confirmed asthe portion having a high concentration of the element other than theportion or the portion having a low concentration of the element thanthe other portion. Since the piezoelectric layer 70 is formed byrepeating the coating process or the burning process in plural times(configured by the plurality of piezoelectric film), by corresponding toeach piezoelectric film, the piezoelectric layer 70 has a plurality ofinterfaces.

In the process, the piezoelectric layer 70 having the laminate structureformed from the same types of the electrode layers or the differenttypes of the electrode layers can be formed. For example, from theviewpoint of obtaining the high orientation, the piezoelectric layer 70may be manufactured by forming the control layer on the underlayer ofthe piezoelectric body, and further forming a main layer of thepiezoelectric body. Each adhesion layer may be provided on the lowermostlayer and the uppermost layer of the piezoelectric layer 70,respectively.

Next, Pt layers 82 a configuring the lower layer side electrode 80 a areformed on the vibrating plate 50 and the piezoelectric layer 70, andafter subjecting the formed layer to a thermal treatment (recoveryanneal (RA) treatment), the piezoelectric layer 70 and the Pt layer 82 aare patterned for each of the piezoelectric element 300 (refer to FIG.3). The Pt layer 82 a is formed by the sputtering method or evaporationmethod. In addition, in the RA treatment, a rapid thermal annealing(RTA) device for heating by radiation of an infrared lamp is used. Here,the Pt layer 82 a is formed by an electrode material which does notgenerate the oxide by the thermal treatment and with high chemicalstability, that is, platinum (Pt). Therefore, an electric resistivitydue to the RA treatment is prevented from being increased and the goodinterface between the upper layer side electrode 80 b to be described(refer to FIGS. 13 and 14) can be formed.

In addition, in the lower layer side electrode 80 a formed of the Ptlayer 82 a, since the electrical properties are not impaired by the RAtreatment, the residual amount of polarization of the piezoelectriclayer 70 is increased and the ferroelectricity is improved. As a result,in a case where the piezoelectric element 300 in which the lower layerside electrode 80 a formed of the Pt layer 82 a is in contact with thepiezoelectric layer 70 is applied to the ultrasonic sensor 1, theexcellent receiving properties can be obtained.

Next, as illustrated in FIGS. 12 to 14, a Ir layer 82 b configuring theupper layer side electrode 80 b is formed on the vibrating plate 50, thefirst electrode layer 60, and the lower layer side electrode 80 a by thesputtering method or the evaporation method. Thereafter, the Ir layer 82b is patterned into a shape that the layer is extended to the outside ofthe piezoelectric element 300 and the space 12 (cavity) in the Xdirection, and the patterned shaped is set as the upper layer sideelectrode 80 b. In addition, as illustrated in FIG. 14, on thepiezoelectric layer 70, the upper layer side electrode 80 b is separatedin the Y direction, the side surface of the piezoelectric layer 70 iscovered from the both end portions of the piezoelectric layer 70, andthe Ir layer 81 b which is extended between the piezoelectric layers 70is patterned. In a portion of a distance L between the second electrodelayer 80, the Pt layer 81 a, and the Ir layer 81 b, the Pt layer 82 a iscut, and the Pt layer 81 a is remained on the both end portions of thepiezoelectric layer 70.

Here, the upper layer side electrode 80 b is formed by an electrodematerial with low electrical resistivity having a tensile stress forimproving the receiving properties, that is, iridium (Ir). For example,in the Ir, iridium oxide (IrO₂) is generated by the RA treatment and theelectric resistivity is improved. The adhesiveness in the Pt interfacethat is the lower layer side electrode 80 a is deteriorated. Therefore,peeling of the electrode is generated. However, these problems can besolved performing the RA treatment before the formation of the upperlayer side electrode 80 b that is after the formation of the lower layerside electrode 80 a.

In addition, since the Ir layer 81 b is provided on the end portion ofthe other piezoelectric layer 70 from one piezoelectric layer 70 in theY direction, it is possible to improve the deformation efficiency bysuppressing the initial deflection to the CAV surface side of thevibrating plate 50 by the Ir layer 81 b. As a result, by adopting thepiezoelectric element 300 having the configuration to the ultrasonicsensor 1, it is possible to obtain the excellent receiving properties.

Furthermore, as illustrated in FIGS. 13 and 14, a resist (notillustrated) is provided on the surface opposite to the piezoelectricelement 300 of the wafer 110, and the resist is subjected to patterninginto a predetermined shape to form a mask film (not illustrated). Thewafer 110 is subjected to anisotropic etching (wet etching) using analkaline solution such as potassium hydroxide (KOH) through the maskfilm. According to this, the space 12 is formed in a region opposite thepiezoelectric element 300 of the substrate 10 (wafer 110).

In addition, a resist (not illustrated) is provided on the surface of awafer 140 (surrounding plate 40), and the resist is subjected topatterning into a predetermined shape to form a mask film (notillustrated). Here, as illustrated in FIG. 2, a mask film (notillustrated) is formed on the edge portion 40 a of the wafer 140 andmask films (not illustrated) which are continuously extended from themask film along the X direction is formed. The wafer 140 is subjected toanisotropic etching (wet etching) using an alkaline solution such aspotassium hydroxide (KOH) through the mask film. Accordingly, thesurrounding plate 40 in which the supporting member 41 and thepiezoelectric element holding portion 32 are formed is manufactured. Inthe wet etching, processing accuracy is deteriorated as compared to adray etching, and a lot of the region can be eliminated at a short time.

Thereafter, the portions are sequentially provided, and the ultrasonicsensor 1 illustrated in FIG. 2 is manufactured. That is, the surroundingplate 40 and the supporting member 41 are bonded to the ultrasonicsensor element 310 with an adhesive (not illustrated) such that thesupporting member 41 is not overlapped with the piezoelectric element300. By providing the sound adjustment layer 13 in the space 12, thelens member 20 is bonded thereto. After bonding the sound adjustmentlayer 13 and the lens member 20, the surrounding plate 40 and thesupporting member 41 may be bonded to the ultrasonic sensor element 310.

EXAMPLES

Hereinafter, examples will be described and the invention will furtherbe described in detail. The invention is not limited to the followingexamples.

Example 1 Preparation of PZT Precursor Solution

A PZT precursor solution was manufactured such that an acetic acid andwater are weighed to a container, and lead acetate, zirconium butoxide,titanium tetra-i-propoxide, and polyethylene glycol were weighed, andthese materials were heated for 90° C. and stirred.

Manufacturing of Vibrating Plate

By thermally oxidizing a silicon substrate (wafer 110) having a size of6 inch, a silicon dioxide film (elastic film 51) was formed on thesubstrate. Next, the zirconium film was formed by the sputtering method,and a zirconium oxide film (insulation layer 52) was obtained by thermaloxidation.

By these processes, the vibrating plate 50 including a silicon dioxidefilm and a zirconium oxide film is manufactured.

Manufacturing of First Electrode Layer

On the vibrating plate 50 (on the zirconium oxide film (insulation layer52)), a titanium layer, a platinum layer, an iridium layer, and atitanium layer were formed in this order by the sputtering method, andthereby manufacturing the first electrode layer 60. In Example 1, thetitanium layer was formed as an adhesion layer for improving theadhesiveness between the layers or the films.

Manufacturing of Piezoelectric Layer (Underlayer)

On the first electrode layer 60, the above-described PZT precursorsolution was coated by the spin coating method, and drying/degreasingwas performed at 140° C. and 370° C., thereby manufacturing a degreasingfilm. A heating process was performed to the degreasing film at 737° C.using a rapid thermal annealing (RTA) device, thereby manufacturing thepiezoelectric layer (underlayer) which is formed of the PZT.

Patterning of First Electrode Layer and Piezoelectric Layer (UnderLayer)

A resist pattern having a predetermined shape was formed on theabove-described piezoelectric layer (underlayer) by a photolithographyand the first electrode layer 60 and the piezoelectric layer(underlayer) was subjected to patterning by the dry etching.

Manufacturing of Control Layer

4 nm of the titanium layer was formed on the piezoelectric layer(underlayer) and the vibrating plate 50 after patterning by thesputtering method. The titanium layer is a control layer for improvingthe orientation of the crystal of the piezoelectric layer (main layer)to be described.

Manufacturing of Piezoelectric Layer (Main Layer)

A coating/drying/degreasing was performed in twice under the samecondition as that of the piezoelectric layer (underlayer) and heatingprocess was performed by the RTA device under the same condition as thatof the piezoelectric layer (underlayer). By performing these operationsat four times, the piezoelectric layer (main layer) was formed on thetitanium layer that is a control layer. According to this, in Example 1,the piezoelectric layer 70 including the piezoelectric layer(underlayer), the titanium layer, and the piezoelectric layer (mainlayer) was obtained.

Manufacturing of Lower Layer Side Electrode

20 nm of a platinum layer (lower layer side electrode 80 a) is formed onthe above-described piezoelectric layer 70 (the piezoelectric layer(main layer)) by the sputtering method. Next, the recovery anneal (RA)treatment was performed at 600° C. for 5 minutes by using the RTAdevice.

Patterning of Titanium Layer, Piezoelectric Layer (Main Layer), andLower Layer Side Electrode

The resist pattern having a predetermined shape was formed on theabove-described platinum layer (lower layer side electrode 80 a) by thephotolithography and the titanium layer, the piezoelectric layer (mainlayer), and the platinum layer were subjected to patterning by the dryetching.

Manufacturing of Upper Layer Side Electrode

30 nm of an iridium layer (upper layer side electrode 80 b) was formedon the platinum layer (lower layer side electrode 80 a) by thepatterning. Next, 15 nm of a titanium layer was formed on the iridiumlayer by the sputtering method. Accordingly, in Example 1, the secondelectrode layer 80 including the platinum layer, the titanium layer, andthe iridium layer was obtained. The titanium layer is an adhesion layerfor overlapping the lead wirings by gold or the like.

Patterning of Upper Layer Side Electrode and Titanium Layer

A resist pattern having a predetermined shape was formed on theabove-described titanium layer by the photolithography and the iridiumlayer (upper layer side electrode 80 b) and the titanium layer weresubjected to the patterning by the dry etching.

In Example 1, by the above processes, the piezoelectric element 300including the first electrode layer 60, the piezoelectric layer 70, andthe second electrode layer which includes the platinum layer (lowerlayer side electrode 80 a) and the iridium layer (upper layer sideelectrode 80 b) was completed.

Formation of CAV Structure

A silicon dioxide film which was formed on a surface opposite to thepiezoelectric element 300 by sandwiching the vibrating plate 50therebetween of a silicon substrate (wafer 110) was removed by grindingprocess and the substrate was grinded and polished so as to make thethickness of the substrate to 400 μm. Next, a chrome (Cr) film having apredetermined shape was formed on the grinded surface, therebymanufacturing a Cr hard mask. In a state where the piezoelectric element300 is subjected to a waterproof treatment, by immersing the substratewith an etching solution including KOH, a cavity (CAV) having apredetermined shape was formed on a surface opposite to thepiezoelectric element 300 by sandwiching the vibrating plate 50 of thesilicon substrate.

In Example 1, by the above processes, a device element A including thepiezoelectric element 300 including the first electrode layer 60, thepiezoelectric layer 70, and the second electrode layer 80 which includesthe platinum layer (lower layer side electrode 80 a) and the iridiumlayer (upper layer side electrode 80 b) in which the CAV is furtherformed was obtained. Here, a device structure of the device element A isdefined as “a”, and an aspect ratio (a ratio of the X direction to the Ydirection) of the moveable portion in the device structure a (a portionsandwiched by the first electrode layer 60 and the second electrodelayer 80) was set to 1:25.

Example 2

In Example 2, by patterning formation which is different from Example 1,patterning of the first electrode layer 60, the piezoelectric layer 70,and the second electrode layer 80 was performed, and the piezoelectricelement 300 including the first electrode layer 60, the piezoelectriclayer 70, and the second electrode layer 80 which includes the platinumlayer (lower layer side electrode 80 a) and the iridium layer (upperlayer side electrode 80 b) was completed.

Thereafter, a silicon dioxide film which was formed on a surfaceopposite to the piezoelectric element 300 with the vibrating plate 50therebetween of a silicon substrate (wafer 110) was removed by grindingprocess and the Si of the silicon substrate was grinded so as to makethe thickness of the substrate to 150 μm, thereby forming the cavity(CAV) having a predetermined shape by the dry etching. Next, a metallicback plate was bonded to the grinded surface with the adhesive so as tocover the CAV. Next, the lens member 20 was bonded to the surface of thevibrating plate 50 side of the silicon substrate through the soundadjustment layer 13. Next, a terminal on the substrate (the firstelectrode layer 60 and the second electrode layer 80) and the terminalon an external circuit board in which a control circuit was providedwere connected by a flexible cable, and a waterproof packaging wasfurther performed by a plastic case, thereby obtaining a device B. Here,a device structure of the device element B was defined as “b”, and anaspect ratio (a ratio of the X direction to the Y direction) of thefunctional portion in the device structure b (a portion sandwiched bythe first electrode layer 60 and the second electrode layer 80) was setto 1:2.

Comparative Example 1

In Comparative Example 1, the device element was manufactured in thesame manner as Example 1 except that the lower layer side electrode 80 ain the second electrode layer 80 was set as 20 nm of the Pt layer andthe upper layer side electrode 80 b is set as 40 nm.

Comparative Example 2

In Comparative Example 2, the device element was manufactured in thesame manner as Example 1 except that the lower layer side electrode 80 ain the second electrode layer 80 was set as the electrode layer in which5 nm of Ti layer was formed on the 4 nm of the Ir layer, and the RAtreatment was performed at 740° C. for 7 minutes.

Comparative Example 3

In Comparative Example 3, the device element was manufactured in thesame manner as Example 2 except that the lower layer side electrode 80 ain the second electrode layer 80 was set as the electrode layer in which5 nm of Ti layer was formed on the 4 nm of the Ir layer, and the RAtreatment was performed at 740° C. for 7 minutes.

Comparative Example 4

In Comparative Example 4, the device element was manufactured in thesame manner as Example 1 except that the lower layer side electrode 80 ain the second electrode layer 80 was set as the electrode layer byforming 5 nm of the Ti layer on the 4 nm of the Ir layer and performingthe RA treatment at 740° C. for 7 minutes, and the upper layer sideelectrode 80 b was set as 20 nm of the Pt layer.

Example 3

In Example 3, the device element was manufactured in the same manner asExample 1 except that a PMN-PT precursor solution was used instead ofthe PZT precursor solution and the manufacturing condition of thepiezoelectric layer was different to Example 1. That was, the deviceelement of Example 3 has the device structure a in which the main layerin the piezoelectric layer 70 is formed of the PMN-PT.

Preparation of PMN-PT Precursor Solution

The PMN-PT precursor solution was manufactured as follows. Firstly,2-butoxyethanol and dimethyl amino ethanol are weighted to a container,thereby manufacturing a mixed solution. Next, titanium tetra-i-propoxideand niobupenta-n-butoxide were weighted in a glove box which was filledwith dry nitrogen, and the resultant was mixed with the mixed solution.Thereafter, after sufficiently stirring the mixed solution at a roomtemperature, magnesium acetate and lead acetate were weighted under theatmosphere, and a mixing/stirring was performed at the room temperature,thereby manufacturing the PMN-PT precursor solution.

Manufacturing of Piezoelectric Layer (Underlayer A)

On the first electrode layer 60, the above-described PZT precursorsolution was coated by the spin coating method, and drying/degreasingwas performed at 140° C. and 370° C., thereby manufacturing a degreasingfilm. A heating process was performed to the degreasing film at 737° C.using a rapid thermal annealing (RTA) device, thereby manufacturing thepiezoelectric layer (underlayer A) which is formed of the PZT.

Patterning of First Electrode Layer and Piezoelectric Layer (UnderlayerA)

A resist pattern having a predetermined shape was formed on theabove-described piezoelectric layer (underlayer A) by a photolithographyand the first electrode layer 60 and the piezoelectric layer (underlayerA) were subjected to patterning by the dry etching.

Manufacturing of Control Layer

4 nm of the titanium layer was formed on the piezoelectric layer(underlayer A) and the vibrating plate 50 after patterning by thesputtering method. The titanium layer is a control layer for improvingthe orientation of the crystal of the piezoelectric layer (main layer)to be described.

Manufacturing of Piezoelectric Layer (Underlayer B)

A coating/drying/degreasing was performed under the same condition asthat of the piezoelectric layer (under layer A), a heating process bythe RTA device was performed under the same condition as that of thepiezoelectric layer (underlayer A), and a piezoelectric layer(underlayer B) was formed on the above-described titanium layer.

Manufacturing of Piezoelectric Layer (Main Layer)

On the piezoelectric layer (underlayer B), the above-described PMN-PTprecursor solution was coated by the spin coating method, anddrying/degreasing was performed at 180° C. and 350° C., therebymanufacturing a degreasing film. A heating process was performed to thedegreasing film at 750° C. using a rapid thermal annealing (RTA) device,thereby manufacturing the piezoelectric film which is formed of thePMN-PT. By repeating the manufacturing process of the piezoelectric filmin 6 times, the piezoelectric layer (the main layer) was formed on thepiezoelectric layer (underlayer B). According to this, in Example 1, thepiezoelectric layer including the piezoelectric layer (underlayer A),the titanium layer, the piezoelectric layer (underlayer B), and thepiezoelectric layer (main layer) was obtained.

Example 4

In Example 4, the device element was manufactured in the same manner asExample 2 except that the manufacturing condition of the piezoelectriclayer was the same as that of Example 3. That is, the device element ofExample 4 has the device structure b in which the main layer in thepiezoelectric layer 70 is formed of the PMN-PT.

Comparative Example 5

In Comparative Example 5, the device element was manufactured in thesame manner as Comparative Example 1 except that the manufacturingcondition of the piezoelectric layer was the same as that of Example 3.

Comparative Example 6

In Comparative Example 6, the device element was manufactured in thesame manner as Comparative Example 2 except that the manufacturingcondition of the piezoelectric layer was the same as that of Example 3.

Comparative Example 7

In Comparative Example 7, the device element was manufactured in thesame manner as Comparative Example 3 except that the manufacturingcondition of the piezoelectric layer was the same as that of Example 3.

Evaluation Content Shape Observation

An appearance configuration (presence or absence of the appearanceabnormal such as laminate state, disconnection, peeling, or the like) ofExamples 1 to 4 and Comparative Examples 1 to 7 was observed by anoptical microscope and a scanning electron microscope (SEM). As aresult, in the device element of Comparative Example 4, the peeling inthe second electrode layer 80 was confirmed, and other than the deviceelement, the special appearance abnormal which affects the propertieswas not observed.

P-E Loop Measurement

Regarding Examples 1 and 3 and Comparative Examples 2 and 6, atriangular wave having a frequency of 1 kHz was applied at roomtemperature by using φ=500 μm of an electrode pattern and a relationship(P-E loop) between a polarization amount P (μC cm²) and a voltage E (V)was obtained through “FCE-1A” manufactured by TOYO corporation. FIG. 15illustrates a P-E loop in which Example 1 was measured at ±25 V. In thesame manner, FIG. 16 illustrates a measurement result of Example 3, FIG.17 illustrates a measurement result of Comparative Example 2, and FIG.18 illustrates a measurement result of Comparative Example 6,respectively. In addition, a residual amount of polarization Pr (μCcm⁻²) which was obtained by the measurement result of each P-E loop isshown in Table 1.

As shown in Table 1, in Example 1 using the Pt as the lower layer sideelectrode 80 a of the second electrode layer 80, the residual amount ofpolarization Pr is 25 μC cm⁻². With respect to this, in ComparativeExample 2 using Ti/Ir as the lower layer side electrode 80 a, theresidual amount of the polarization Pr is 22.7 μC cm⁻². That is, inExample 1, the residual amount of polarization Pr is increased by about10% compared to Comparative Example 2.

In addition, as shown in Table 1, in Example 3 using the Pt as the lowerlayer side electrode 80 a of the second electrode layer 80, the residualamount of polarization Pr is 14.6 μC cm⁻². With respect to this, inComparative Example 6 using the Ti/Ir as the lower layer side electrode80 a, the residual amount of polarization Pr is 4.3 μC cm⁻². That is, inExample 3, the residual amount of polarization Pr is increased about 3times compared to Comparative Example 6.

From the above description, it is clear that by using the Pt to thelower layer side electrode 80 a, the ferroelectricity of the deviceelement can be improved. In addition, it is clear that an improvementeffect of the ferroelectricity can receive the full benefit regardlessof the electronic structure.

Initial Deflection Measurement

Regarding Examples 1 to 4 and Comparative Examples 1 to 7, a deflectionamount (initial deflection amount) in a non-voltage applied state wasmeasured through an optical interferometric surface roughness measuringsystem “NT9300DMEMS” manufactured by Veeco Instruments Inc. In FIG. 19,a schematic diagram of a state where the shape is deflected in a convexshape with respect to the CAV (space 12) of the device element(hereinafter, referred to as a “convex deflection”) is shown and in FIG.20, a schematic diagram of a state where the shape is deflected in aconcave shape with respect to the CAV (space 12) of the device element(hereinafter, referred to as a “concave deflection”) is shown. Inaddition, each of the initial deflection measurement results is shown inTable 1. In Table 1, a case of no deflection is indicated as zero, aninitial deflection amount d of a case of the convex deflection (refer toFIG. 19) is indicated as +d, and the initial deflection amount d of acase of the concave deflection (refer to FIG. 20) is indicated as −d.

As shown in Table 1, in Comparative Example 2 using the Ti/Ir to theboth of the lower layer side electrode 80 a and the upper layer sideelectrode 80 b of the second electrode layer 80, it becomes the convexdeflection having the initial deflection amount d of +11 nm. That is, inComparative Example 2, since the Ir mainly applies the tensile stress inin-plane direction with respect to the piezoelectric element 300 and thevibrating plate 50, and the balance between a compressive stress to beapplied to the vibrating plate 50 by the piezoelectric element 300 canbe established, it becomes +11 nm of the convex deflection.

On the other hand, in Comparative Example 1 in which the Pt is used forthe lower layer side electrode 80 a and the upper layer side electrode80 b is not formed, it becomes the concave deflection having the initialdeflection amount d of −214 nm. That is, in Comparative Example 1, sincein-plane stress to be applied to the piezoelectric element 300 and thevibrating plate 50 by the Pt is small, and the compressive stress to beapplied to the vibrating plate 50 by the piezoelectric element 300 isdominant, it becomes −214 nm of the concave deflection.

With respect to this, in Example 1 using the Pt to the lower layer sideelectrode 80 a and using the Ti/Ir to the upper layer side electrode 80b, the initial deflection amount d becomes 0 nm, and an initialdeflection position is greatly improved with respect to ComparativeExample 1.

In addition, as shown in Table 1, in Comparative Example 6 using theTi/Ir to both of the lower layer side electrode 80 a and the upper layerside electrode 80 b of the second electrode layer 80, it becomes anconcave deflection having the initial deflection amount d of −57 nm.That is, in Comparative Example 6, since the Ir mainly applies thetensile stress in in-plane direction with respect to the piezoelectricelement 300 and the vibrating plate 50, and the balance between acompressive stress to be applied to the vibrating plate 50 by thepiezoelectric element 300 can be established, it becomes −57 nm of theconcave deflection.

On the other hand, in Comparative Example 5 in which the Pt is used forthe lower layer side electrode 80 a and the upper layer side electrode80 b is not formed, it becomes the concave deflection having the initialdeflection amount d of −159 nm. That is, in Comparative Example 5, sincein-plane stress to be applied to the piezoelectric element 300 and thevibrating plate 50 by the Pt is small, and the compressive stress to beapplied to the vibrating plate 50 by the piezoelectric element 300 isdominant, it becomes −159 nm of the concave deflection.

With respect to this, in Example 3 using the Pt to the lower layer sideelectrode 80 a and using the Ti/Ir to the upper layer side electrode 80b, it becomes the concave deflection having the initial deflectionamount d of −76 nm, and an initial deflection position is greatlyimproved with respect to Comparative Example 5.

From the above-described results, it is clear that by setting the upperlayer side electrode 80 b as the Ti/Ir without any change of the Ptwhich is used as the lower layer side electrode 80 a, the initialdeflection is greatly improved. In addition, it is clear that animprovement effect of the initial deflection can receive the fullbenefit regardless of the electronic structure. In addition, asdescribed above, Ti of the upper layer side electrode 80 b is theadhesion layer for overlapping the lead wirings by Au or the like. Theformation of Ti has no negative effects on the tensile stress of the Ir.

In addition, by the problem of the pattern shape, the initial deflectionamounts d of Examples 2 and 4 and Comparative Examples 3 and 7 cannot bemeasured. However, it is found that by observing the appearance, itbecomes the deflection shape that Example 2 is follows Example 1,Example 4 is follows Example 3, Comparative Example 3 is followsComparative Example 2, and Comparative Example 7 is follows ComparativeExample 6.

Transmitting and Receiving Properties

In FIG. 21, a diagram for illustrating an evaluation method of thetransmitting and receiving properties is illustrated. As illustrated inFIG. 21, the transmitting and receiving properties were measured usingan evaluation machine 400, an ultrasonic element 401, and an SUS plate402. In Examples 1 and 2 and Comparative Examples 1 to 4, an evaluationof 6 MHz of the transmitting and receiving properties in water wasperformed, and in Examples 3 and 4 and Comparative Examples 5 to 8, anevaluation of 5.5 MHz of the transmitting and receiving properties inthe water was performed.

Here, the transmitting and receiving properties are properties of thereceiving voltage generated when a longitudinal wave W1 which is sent byinserting ±6 V of waveform under a DC 10 V by the ultrasonic element 401inserted into the water is reflected to a SUS plate (SUS plate 402)which is mounted ahead of 20 mm and a reflected wave W2 is received bythe same element (ultrasonic element 401).

In FIG. 22, transmitting and receiving voltages of Example 2 and Example3 are illustrated, and in FIG. 23, transmitting and receiving voltagesof Example 4 and Example 7 are illustrated. As illustrated in FIG. 22,the transmitting and receiving voltage of Comparative Example 3 usingthe Ti/Ir to the lower layer side electrode 80 a is 32.3 mV. Withrespect to this, the transmitting and receiving voltage of Example 2using the Pt to the lower layer side electrode 80 a is 36.6 mV, and itis clear that the voltage is improved by about 13%. In the same manner,as illustrated in FIG. 23, in compared to Comparative Example 7 in whichthe Ti/Ir is used for the lower layer side electrode 80 a, it is clearthat the transmitting and receiving voltage of Example 4 using the Pt tothe lower layer side electrode 80 a is largely improved and goodtransmission and reception sensitivity is exhibited.

From the result, it is clear that a configuration of the devices ofExamples 2 and 4 in which the ferroelectricity is improved by using thePt to the lower layer side electrode 80 a, and the initial deflection isimproved by using the Ti/Ir to the upper layer side electrode 80 b andwhich is provided so as to extend to the outside of the piezoelectricelement 300 and the space 12 (cavity) across the X and Y directions isappropriate to the ultrasonic device.

Relationship Between Deflection Shape and Transmitting and ReceivingProperties

In FIG. 24, a relationship between the deflection shape and thetransmitting and receiving properties which is calculated by thesimulation is illustrated. As illustrated in FIG. 24, in a range of theinitial deflection amount d of 0 nm to +200 nm, there is almost noeffect on the transmitting and receiving sensitivity. With respect tothis, it is found that in a case where the initial deflection amount dis less than 0 nm, the transmitting and receiving sensitivity isdeteriorated according to the amount. That is, in comparison of Example2 that is a configuration of the second electrode layer 80 as the samemanner of Example 1 and Comparative Example 3 that is a configuration asthe same manner of Comparative Example 2, it is clear that it is notrequired for considering the difference between the initial deflections.

In addition, in Example 2 and Comparative Example 3, the initialdeflection amount could not be measured. However, in the P-E loopmeasurement, when it is considered that in Example 1 corresponding toExample 2, the residual amount of polarization Pr is improved by 10% ascompared to Comparative Example 2 corresponding to Comparative Example3, the reason of the improve in the transmitting and receivingsensitivity in Example 2 by 13% is that the residual amount ofpolarization Pr is improved as compared to Example 3.

Furthermore, as shown in Comparative Example 1, in a case where the Ptis used for the lower layer side electrode 80 a and the upper layer sideelectrode 80 b is not formed, as shown in Table 1, since the initialdeflection amount d is −214 nm, it is found from FIG. 24 that negativeeffects was caused by the tensile stress.

Accordingly, by setting the lower layer side electrode 80 a as the Pt,and setting the upper layer side electrode 80 b as the Ti/Ir, it isclear that the negative effect caused by that the initial deflection isconcaved can be avoided.

TABLE 1 Piezo- Residual electric Second Electrode Layer Initial Amountof Device Layer (Lower (Upper Deflection Polarization Struc- (Main layerside layer side Initial Amount d Pr ture layer) electrode) electrode)Peeling Deflection nm μC cm⁻² Example 1 a PZT Pt Ti/Ir Absence None 0 25Example 2 b Pt Ti/Ir Absence None — — Comparative a Pt — Absence Concave−214 — Example 1 Comparative a Ti/Ir Ti/Ir Absence Convex +11 22.7Example 2 Comparative b Ti/Ir Ti/Ir Absence Convex — — Example 3Comparative a Ti/Ir Pt Present — — — Example 4 Example 3 a PMN-PT PtTi/Ir Absence Concave −76 14.6 Example 4 b Pt Ti/Ir Absence Concave — —Comparative a Pt — Absence Concave −159 — Example 5 Comparative a Ti/IrTi/Ir Absence Concave −57 4.3 Example 6 Comparative b Ti/Ir Ti/IrAbsence Concave — — Example 7

As described above, according to the piezoelectric element 300 ofExamples 1 to 4, the residual amount of polarization is increased bycontacting the Pt layer that is the lower layer side electrode 80 a withthe piezoelectric layer 70, thereby improving the ferroelectricity.Furthermore, the initial deflection to the CAV surface side of thevibrating plate 50 is suppressed by the tensile stress of the Ir of theTi/Ir layer that is the upper layer side electrode 80 b which isprovided so as to extend to the outside of the piezoelectric element 300and the space 12 (cavity) across the X and Y directions, therebyimproving the deformation efficiency. As a result, it is clear that thepiezoelectric element 300 of Examples 1 to 4 is the ultrasonic devicewith excellent receiving properties.

Other Embodiments

In the above-described embodiments, a lens structure having a type(so-called CAV surface type) in which the side opposite to thepiezoelectric element of the vibrating plate is set as the passing areaof the ultrasonic waves is applied. However, the structure is notlimited thereto. For example, the lens structure having a type(so-called ACT surface type) in which the piezoelectric element side ofthe vibrating plate is set as the passing area of the ultrasonic wavesmay be applied depending on the application.

In addition to the above-described present embodiment, an ultrasonicmeasurement device can be configured by equipping the piezoelectricelement 300 according to the invention and a control unit for measuringthe detection object by using the signal based on at least one of theultrasonic wave which is sent by the piezoelectric element 300 and theultrasonic waves which is received by the piezoelectric element 300.

Such an ultrasonic measurement device obtains information relating to aposition, a shape, a speed, or the like of the measurement object baseda time from a time point in which the ultrasonic waves is sent to thetime point in which the echo signals in which the sent ultrasonic wavesare reflected to the measurement object and are returned, and thepiezoelectric element 300 is used as an element for generating theultrasonic waves or an element for sensing the echo signals. If thepiezoelectric element 300 according to the invention which obtains theimprovement in the piezoelectric constant is used as an ultrasonicgenerating element or an echo signal sensor, the ultrasonic measurementdevice with the improved ultrasonic generating efficiency or echo signalsensing efficiency can be provided.

Although not described in the above-described present embodiment, forexample, it can provide a configuration in which a side opposite to thepiezoelectric element 300 of the vibrating plate 50 is set as thepassing area of the ultrasonic waves which are sent toward themeasurement object or the ultrasonic waves (echo signals) which arereflected from the measurement object. According to this, aconfiguration of a side opposite to the piezoelectric element 300 of thevibrating plate 50 can be simplified and the good passing area of theultrasonic waves can be maintained. In addition, an electrical region ofan electrode, a wiring, or the like, or an adhesion fixed region of eachportion is apart from the measurement object. Accordingly, contaminationor leakage current between these regions and the measurement objects canbe easily prevented. Accordingly, the invention can also beappropriately applied to a medical instrument which specifically resentthe contamination or the leakage current, for example, an ultrasounddiagnostic device, a hemopiezometer, and an ophthalmotonometer.

In addition, although not described in the above-described presentembodiment, it is preferable that a sealing plate for sealing a regionincluding the piezoelectric element 300 is bonded to the substrate 10.According to this, since the piezoelectric element 300 can be physicallyprotected, and strength of the ultrasonic sensor 1 is increased, it ispossible to improve the structure stability. Furthermore, in a casewhere the piezoelectric element 300 is configured as a thin film,handling properties of the ultrasonic sensor 1 including thepiezoelectric element 300 can be improved.

In the present embodiment, the space 12 is illustrated as an example inwhich the space 12 is formed for each piezoelectric element 300.However, it is not limited thereto, and the space 12 may be formed inaccordance with the plurality of piezoelectric elements 300. Forexample, the spaces 12 which are in common to the row of thepiezoelectric elements 300 that are arranged along the scan direction,or one space 12 may be entirely formed. In a case where the spaces 12which are common to plurality of piezoelectric elements 300 areprovided, the vibrating states of the piezoelectric element 300 aredifferent. However, by providing the member for pressing between thepiezoelectric elements 300 from the side opposite to the substrate 10 ofthe vibrating plate 50 and the same vibrating as that of the case wherethe separated space 12 is provided may be performed.

Here, an example of an ultrasonic diagnosis device using theabove-described ultrasonic sensor will be described. FIG. 25 is aperspective view illustrating a schematic configuration of an example ofthe ultrasonic diagnosis device and FIG. 26 is a side view of theultrasonic probe.

As illustrated in the drawing, an ultrasonic diagnosis device 101includes a device terminal 102 and an ultrasonic probe (probe) 103. Thedevice terminal 102 and the ultrasonic probe 103 are connected to eachother by a cable 104. Electrical signals are received and transmittedbetween the device terminal 102 and the ultrasonic probe 103 through thecable 104. A display panel (display device) 105 is assembled in thedevice terminal 102. A screen of the display panel 105 is exposed to thesurface of the device terminal 102. An image based on the ultrasonicwaves which are transmitted from the ultrasonic sensor 1 of theultrasonic probe 103 and detected is generated in the device terminal102. The imaged detection result is displayed on the screen of thedisplay panel 105.

As illustrated in FIG. 26, the ultrasonic probe 103 includes a housing106. The ultrasonic sensor 1 in which a plurality of ultrasonic sensorelements 310 (refer to FIG. 2) are arranged two dimensionally in the Xdirection and the Y direction is stored in the housing 106. Theultrasonic sensor 1 is provided such that the surface of the ultrasonicsensor 1 is exposed to the surface of the housing 106. The ultrasonicsensor 1 outputs the ultrasonic waves from the surface and receives thereflected waves of the ultrasonic waves. In addition, the ultrasonicprobe 103 can include a probe head 103 b which is detachable to a probemain body 103 a. In this case, the ultrasonic sensor 1 can be assembledinto the housing 106 of the probe head 103 b. The ultrasonic sensor 1 isconfigured such that the ultrasonic sensor elements 310 are arranged twodimensionally in the X direction and the Y direction.

The entire disclosure of Japanese Patent Application No. 2015-246728,filed on Dec. 17, 2015 is expressly incorporated by reference herein.

What is claimed is:
 1. A piezoelectric device for an ultrasonic sensorcomprising: a substrate with a cavity; a vibrating plate which isprovided on the substrate so as to block an opening surface of thecavity; and a piezoelectric element which is provided on a surface ofthe vibrating plate opposite to the cavity, including a first electrodea piezoelectric layer which is provided on the first electrode, and asecond electrode which is provided on the piezoelectric layer, whereinthe second electrode has a laminated structure including a platinumlayer and an iridium layer, wherein the platinum layer is in contactwith the piezoelectric layer, and wherein, if it is assumed that twodirections which are parallel to a surface of the substrate and mutuallyperpendicular are defined as an X direction and a Y direction, theiridium layer is extended to an outside of the piezoelectric element andthe cavity at least in the X direction on an X-Y plane view.
 2. Thepiezoelectric device for an ultrasonic sensor according to claim 1,wherein the piezoelectric layer is present in the cavity, and whereinthe platinum layer is present only on the piezoelectric layer in the Xdirection.
 3. The piezoelectric device for an ultrasonic sensoraccording to claim 1, wherein a second iridium layer is extended to theoutside of the piezoelectric element and the cavity in the Y directionon the X-Y plane view, and wherein the second iridium layer is separatedfrom the iridium layer, on the piezoelectric layer.
 4. The piezoelectricdevice for an ultrasonic sensor according to claim 3, wherein thepiezoelectric layer is present in the cavity, and wherein the secondiridium layer is extended from both end portions on the piezoelectriclayer to the outside of the cavity in the Y direction, and a secondplatinum layer which is separated from the platinum layer is presentbetween the both end portions of the piezoelectric layer and the secondiridium layer.